1. Field of the Invention
The present invention relates to a mobile telephone, personal digital assistant (PDA), game machine, or other information terminal device used in various information communications.
2. Description of the Related Art
A conventional information terminal device will be explained by referring to FIG. 6. FIG. 6 is a front view of a conventional information terminal device. The information terminal device shown in FIG. 6 is a foldable mobile telephone, shown in an unfolded state.
In FIG. 6, conventional information terminal device 510 comprises upper case 520, lower case 530, and main body case 550 coupling them by means of linkage 540. Upper case 520 includes rectangular video display unit 560 provided on the front side, and audio output units 571, 572 provided on the same plane as video display unit 560. These audio output units 571, 572 are speakers disposed closely to the two corners of the upper case 520 at opposite ends of a diagonal of video display unit 560. One channel of stereophonic sound is reproduced from one speaker, and another channel of stereophonic sound is reproduced from the other one.
A conventional information terminal device similar to device 510 is disclosed, for example, in Japanese Patent Publication No. 2003-78601 (unexamined).
However, an information terminal device having such conventional configuration has difficulty reproducing reality and presence by stereophonic acoustics in stereophonic sound reproduction.
A cause of the difficulty is disagreement between video localization of video display unit 560 and audio localization in a vertical direction of audio output units 571, 572. Audio output units 571, 572 are disposed closely to the two corners at opposite ends of a diagonal of video display unit 560. That is, audio output units 571, 572 are disposed symmetrical in a diagonal form with respect to video display unit 560.
At times, the audio localization of audio output units 571, 572 is in the center of a straight line linking the two speakers. The straight line linking the audio output units 571, 572 is nearly parallel to a diagonal of upper case 520. The video localization of video display unit 560 is also in the center of the rectangular screen, and the video localization coincides with the audio localization. However, this coincidence of video localization and audio localization only occurs when the output sound pressure levels from the right and left speakers are equal to each other. In this limited condition, the sound is localized midway between the right and left speakers, and coincides with the video localization of video display unit 560. In reality, however, the speakers are very rarely operated in such condition.
When audio data is reproduced from audio output units 571, 572, the changing of audio signals at every moment always causes output sound pressure level differences between the right and left speakers. When output sound pressure level differences are caused between the right and left speakers, the sound is not localized in the center of the screen, and is deviated toward the speaker of higher sound pressure level. Due to difference in sound pressure levels of the right and left speakers, the sound comes to have a depth, and the audio localization can be moved along with the video localization.
However, when the audio localization moves on the straight line between the right and left speakers due to such change in sound pressure levels, since the straight line linking the right and left speakers is not horizontal, a problem lies in localization in the vertical direction. That is, the audio localization is also moved in the vertical direction by the portion of deviation from the center to either the upper or the lower side. This is sensed because the human audible sense works in both the lateral direction and the vertical direction.
Therefore, for the user of the information terminal device, the video localization of the video display unit and the audio localization of the audio output units do not coincide in the vertical direction. That is, the direction sense to video and the direction sense to audio do not coincide, and strangeness is felt in hearing sensation. As a result, the conventional information terminal can hardly satisfy the reality and presence by stereophonic acoustics in stereophonic reproduction.